Up to now, it's all been hippie-talk. Let's get back to the earth, they all say. It's good for your body and good for your spirit. And it not just the hippies either. Native people have always advocated contact with the Earth, for reasons of their own. Walk barefoot on the ground and stay in touch with the source of life.
Well now it's time for science to get into the act. As it turns out, there's an actual physical-biological connection between dirt and performance. We've known for a long time that contact with soil bacteria primes the immune system to "learn" about foreign pathogens. This "hygiene hypothesis" suggests that our modern super-clean, insulated style of living is actually dangerous for our bodies and may promote diseases such as asthma.

But it's more than just immunity. Two recent studies have found strong associations between dirt and mental performance. Mycobacterium vaccae is a natural soil bacterium that appears to increase cognitive performance in rodents, probably by affecting the serotonin system. It also appears to elevate mood, similar to the effect of an anti-depressant.

Of course, from a natural-history perspective, this all fits. Since humans evolved in high-touch natural environments, it makes sense to suppose that our bodies would be massively connected to the microbial world. When we sever that contact as we've done with modern barriers and insulation, we should not be surprised to find a wide-range of negative effects on our bodies. These discoveries are just the beginning.

So take your shoes off and do some barefooting this summer. Your body wants dirt.